This invention relates to a bioelectrode structure and method for delivering chemical species into a person's skin or across the skin barrier.
The use of bioelectrodes for non-invasive delivery of chemical species into or through skin is known. Such bioelectrodes typically include an open receptacle having a generally planar base for holding the fluid to be iontophoresed, one electrode carried within the receptacle for maintaining electrical contact with the fluid, and a second electrode for contacting the skin to produce a potential gradient between the skin and the fluid in the receptacle. Often times the receptacle is fairly rigid to define a rigid perimeter about the opening. The opening in the receptacle is positioned over the skin and then fluid, containing the chemical species, is introduced into the receptacle to contact the skin. When the potential gradient is established, the chemical species migrates into the skin.
Because the prior art receptacles include openings through which the fluid flows to the skin, it is important that a tight seal between the skin and the sealing lip around the opening be maintained to prevent leaking of fluid. This leaking problem is exacerbated when the receptacle must be placed against an especially irregular skin surface because of the difficulty of conforming the typically planar contact base portion of the receptacle with the skin surface. Further, when the receptacle is removed from the skin following an injection, unused fluid may drip from the receptacle opening. This loss of fluid is both wasteful and messy.
It has been suggested that a wicking material be placed over the opening of the bioelectrode receptacle to improve the uniformity of contact between the fluid and the skin surface. Such an arrangement although reducing spillage, does not allow retention and storage of the fluid in the receptacle since, if fluid were introduced into the receptacle long prior to use, the fluid would tend to flow through and evaporate from the wicking material. Also, any substantial pressure on a filled receptacle would tend to accelerate the flow of fluid through and out of the wicking material. See U.S. application Ser. No. 851,082, now U.S. Pat. Ser. No. 4,166,457.
In addition to the above problems, currently used bioelectrodes typically include an electrode element positioned within the receptacle. This configuration insures good electrical contact between the element and the fluid in the receptacle, but introduces another potential source of leakage at the situs in the receptacle wall through which the electrode or electrode connector extends.
Examples of prior art electrodes are described in U.S. Pat. No. 3,862,633, 3,945,384 and 3,973,557. Exemplary prior art apparatus for transferring microorganisms through the skin is disclosed in U.S. Pat. No. 4,100,920.